Forces loyal to President Bashar al Assad have reportedly used helicopter gunfire and mortars in the battle for Aleppo, amid fresh claims British intelligence is helping rebel fighters to oust the Syrian leader.

According to an opposition official, information on Syrian troop movements is helping rebels launch successful attacks on regime forces in the second city, where both sides have been locked in fierce fighting for weeks.

"British intelligence is observing things closely from Cyprus," the official told The Sunday Times.

"It's very useful because they find out a great deal.

"The British are giving the information to the Turks and the Americans and we are getting it from the Turks."

Protesters against the Assad regime in Idlib

The newspaper quoted the official as saying British authorities "know about and approve 100%" intelligence from their Cyprus military bases being passed through Turkey to the rebel troops of the Free Syrian Army (FSA).

"The British monitor communications about movements of the government army and we got information about reinforcements being on their way to Aleppo," the official continued.

"We hit at the government troops in Idlib and Saraqib (southwest of Aleppo), with success."

It is the first indication that British intelligence is playing a covert role in the anti-regime revolt.

Aleppo - the country's commercial centre - has become the focus of the 17-month conflict, partly because of its strategic location near the Turkish border.

Meanwhile, Christians in Damascus have been telling Sky Foreign Affairs Editor Tim Marshall of their fears for the future as bloodhshed threatens the country's secular society.

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The patriarch of a Greek Catholic church in the Syrian capital says some Christians fear they could be forced out of the country after a civil war, as has happened in other countries touched by Arab Spring unrest.

Syrian state TV has aired footage of President Assad at a mosque in Damascus.

In his first public appearance since the beginning of July, Mr Assad attended a prayer service to mark the start of Eid.

On Saturday, opposition fighters clashed with Syrian troops close to the city's airport.